1. Field
Example embodiments relate in general to ski boots, and more specifically, to a ski boot assembly having an outer shell that accommodates an inner shoe.
2. Discussion of Related Art
Conventional ski boots include a rigid outer shell, which is typically fabricated from plastic materials. The rigid outer shell performs two basic functions. First, the outer shell anchors the foot to the ski via a ski binding. Second, the outer shell strengthens and supports the connection between the lower leg and the foot so that movements in the lower leg are transmitted efficiently to the foot and ski. A loose or sloppy fit may reduce efficiency by requiring a larger movement or greater effort to produce a given result. Accordingly, a close and tight fit is desirable.
Although existing ski boots have enjoyed widespread use, they are not without shortcomings. For example, a rigid outer shell may not conform well to the multitude of foot shapes, which makes the boots uncomfortable. Moreover, the plastic of the outer shell may stiffen in cold weather with the result that it can be difficult and even painful to remove one's foot from the boot.
Most manufacturers use an inner liner, which is a soft layer, to provide a buffer between the shell and the skier's foot. A variety of methods and materials have been devised for this buffer, but many skiers find that boots are uncomfortable, especially over an extended length of time. Some liners offer a closer fit by molding with the use of heat. But moldable liners are more expensive, and they do not solve the problem of the outer shell stiffening in cold weather. Despite these problems, the majority of commercially available boots retain the rigid outer shell.
To provide the desired connection between the lower leg and the ski, conventional designs extend the rigid outer shell above the ankle to the lower leg and employ a cuff around the shell with a pivot point at the ankle. The cuff, in combination with the outer shell, strengthens the connection between the lower leg and the ski so that skiers can put substantial pressure on the ski to achieve precise carving turns. A problem with the conventional combination of the cuff and the outer shell is that different degrees of restriction in the flex movement of the ankle are desirable for different types of skiing and different levels of ability. Usually, stiffer boots are desired by more experienced skiers. The degree of stiffness is determined primarily by the type of plastic used in the outer shell, and each model has a given degree of resistance. Usually the stiffer boots are more expensive. Even so, all models tend to stiffen in cold weather.
Conventional ski boots are also heavy and awkward to walk in. Some liners are removable from the outer shell. But the liners are not designed for walking. For example, a liner may have smooth sole to mate with the corresponding smooth inner surface of the outer shell, and this can lead to slipping.
In an attempt to increase comfort, some assemblies have been proposed in which a flexible shoe or boot is mounted to a rigid plate or outer frame. But such assemblies have resulted in unwanted relative movements between the foot and the ski. Any looseness of the foot within the walking boot or any relative movement between the walking boot and the outer frame reduces the efficiency of motion control in skiing. Looseness in the forefoot area is detrimental when skiers engage in swiveling movements in the horizontal plane (when skiing in moguls, for example). Looseness in the heel area is detrimental when the heel tends to slip up relative to the boot sole when the skier leans forward.
Conventional assemblies also fail to properly connect the lower leg to the ski. The problem of connecting the lower leg to the ski centers on movement in the ankle. Looseness in the connection between the lower leg and the foot occurs naturally because, even when the tibia is held completely still, the ankle allows the foot to move in a variety of ways. Specifically, the foot can rotate around the three axes of space passing through the ankle, the natural pivot point. The foot can rotate around the vertical axis (one can swivel one's forefoot left or right), the foot can rotate around the lateral axis (one can raise or lower one's foot), and the foot can rotate around the longitudinal axis (one can twist one's foot clockwise or counter clockwise). Ski boots help skiers achieve a competent performance by allowing some movements but restricting others. The boot should allow the natural movement about the vertical axis, limit the movement about the lateral axis in a specific manner, and prevent movement about the longitudinal axis. To provide this set of characteristics along with comfort, efficiency, and simplicity has proved difficult. This challenge has led to complicated structures. For example, some conventional structures incorporate a complex torsion spring made of rubber. Complex designs are likely to increase the cost of manufacture. There are some simpler designs. But here, levers are attached at the lower end to the heels of shoes and extend rather high on the leg to be attached to the upper calf with straps. These conventional structures create a pivot point for the lever that does not coincide with the ankle, the natural pivot of the foot. This disparity creates discomfort by pushing the strap up or down on the calf when the skier leans forward or returns to a more upright stance. The high placement of the strap up to and including the knee makes it extremely difficult to put the whole assembly on one's foot and leg when one is wearing the normal ski pants. Furthermore, in some conventional assemblies, the shoes cannot be removed from the surrounding structure in order to walk easily. In other assemblies, the shoe can be inserted and withdrawn from the outer shell. But the ease of entry comes at the cost of a substantial reduction in the resistance to forward lean. Furthermore, the design does not provide the ability to adjust the boot for skiers who may be somewhat bowlegged or knock-kneed.